FIG. 4 shows an example of a conventional waterproof structure for a portion where members are tightened with a screw. FIG. 4 shows a state of a tightening section where a first member 10 and a second member 11 are fastened with a bolt 12, the tightening section being cut out by a plane passing through a central axis of the bolt 12.
In the first member 10, a screw hole 10a with a bottom is provided, and in the second member 11, a screw insertion hole 11a is provided. The second member 11 is fastened to the first member 10 by screwing the bolt 12 which passes through the screw insertion hole 11a into the screw hole 10a with a bottom.
Then, to form a waterproof structure, a spacer 13 and a packing 14 are placed between the bolt 12 and the second member 11. In addition, FIG. 4 exaggeratedly shows a state in a larger scale before the packing 14 is deformed. A ring-like packing 14 having a rectangular cross-section made of rubber is fitted in a dent of the spacer 13 made of metal and placed on the screw insertion hole 11a of the second member 11 mounted on the first member 10, and the bolt 12 is inserted into the packing 14 to be tightly screwed into the screw hole 10a with a bottom.
A lower surface of the spacer 13 is pressed against an upper surface of the second member 11 by tightening up the bolt 12, and further the packing 14 is compressed and pressed against an inner surface of the spacer 13, an outer surface of the bolt 12 and the upper surface of the second member 11, providing a waterproof property.
In the conventional waterproof structure for a portion where members are tightened with a screw described above shown in FIG. 4, a bottom surface of the spacer 13 is arranged to abut on the upper surface of the second member 11 for positioning in the vertical direction, which has presented a problem that the surface of the second member 11 was scraped away, when it was made of resin. Also, the packing 14 gets entangled with a screw portion of the bolt 12, which leads to a problem that the packing 14 becomes unusable, when the bolt 12 is repeatedly tightened.
Further, because the packing 14 gets entangled with the screw portion of the bolt 12 in a process of tightening the bolt 12, the spacer 13 and the packing 14 are rotated together with the bolt 12, so that there arises a problem that the packing 14 is likely to be deformed.
Also, because lower surfaces of the spacer 13 and the packing 14 are arranged to abut on the upper surface of the second member 11, the upper surface of the second member 11 has to be a horizontal surface. Then, because a head of the bolt 12 is mounted on the upper surface of the second member 11, the spacer 13 and the head of the bolt are protruded from the upper surface of the second member 11, presenting a problem of requiring a larger, necessary space.
In a waterproof structure for apparatuses proposed in Japanese Patent Application Laid-Open No. 2000-277934, a first boss 33 is provided in a front case 31 in a protruding manner toward a rear case 41, and a second boss 43 is provided in a protruding manner in the rear case 41 to be opposite to the first boss 33.
Then, a through hole 44 is made into the second boss 43 to insert a fixing screw 55 thereinto, and a hole 34 with a bottom is made into the first boss 33 to screw the fixing screw 55 thereto. Also, an annular groove 45 coaxial with the through hole 44 is formed in a surface of the second boss 43 opposite to the first boss 33, and an O-ring 46 is positioned in this annular groove 45.
On the one hand, in a surface of the first boss 33 opposite to the second boss 43, an annular projection 35 is formed to be opposite to the annular groove 45. Then, when the front case 31 and the rear case 41 are fitted in each other, the annular projection 35 is arranged to press the O-ring 46.
In the waterproof structure for apparatuses proposed in Japanese Patent Application Laid-Open No. 2000-277934 described above, because the O-ring 46 is pressed by the annular projection 35, too strong fastening force on the fixing screw 55 may damage the O-ring 46, causing a problem that the O-ring cannot be repeatedly used.